According to recent reports, Israel estimates that Iran is working to move weapons to Hezbollah in Lebanon by sea in response to attacks on similar weapons shipments overland via Syria. What can Israel do to counter these shipments, and is international law – just by chance – in its favor?This question immediately calls to mind the recent capture of the Iranian oil tanker Grace 1 by Gibraltar authorities and the British Royal Navy on the suspicion that it was headed for Syria, in defiance of European Union sanctions, which in turn resulted in the capture of a British tanker by Iran. This incident demands a discussion of very complex questions, including the applicability in Gibraltar of the sanctions imposed on Syria by the European Union, the right to freedom of navigation in international waterways, and the question of the country to which the tanker was registered.In the case of marine weapons shipments from Iran to Hezbollah, the legal situation is simpler and clearer: United Nations Security Council Resolution 1701, which was passed at the end of the Second Lebanon War (2006) and is binding on all countries, requires that states take all necessary measures to prevent the supply or sale of military equipment to any individual or entity in Lebanon by their nationals or from their territories or using their flag vessels or aircraft. The only exceptions to this ban are the Lebanese army and UNIFIL.In fact, Israel can halt these shipments even without using military force, with such use of force running the risk of incurring retaliatory actions, as occurred in the British case. If Israeli intelligence services have concrete information that military equipment destined for Hezbollah is aboard a certain ship, Israel can inform the country to which the ship is registered, the countries in which the ship is due to dock, and the countries whose citizens (including corporations registered in those countries) are involved in transferring the shipment. These countries are entitled and obligated to check these claims, and if the suspicions are confirmed, to prevent the transfer of this materiel to Lebanon and Hezbollah, which would be a contravention of the UN Security Council resolution.Clearly, states do not always fulfill their obligations, and of course, in cases where an Israeli military operation is being considered, there is a risk that informing another country might endanger such an operation. However, military action is not always practical or politically desirable. In these cases, why should Israel not try this option?Iran can attempt to limit the risk of its arms shipments to Hezbollah being captured by using ships under its flag and sailing in open seas directly from Iran to Lebanon without any other country gaining the power accrued from using its ships or passing through its waters. However, this course imposes significant practical constraints on carrying out these shipments, and also makes it easy to track and uncover Iranian actions contravening the UN resolution. Thus, even forcing Iran to take such a course of action gives Israel an advantage.Another way of circumventing the ban imposed by Resolution 1701, which would involve cooperation with the Lebanese government, would be to designate the Lebanese military as the official end-receiver of military shipments and then to transfer these to Hezbollah. Given Hezbollah’s influence and involvement in the Lebanese regime, this would certainly seem possible. However, this course of action would also be advantageous from Israel’s perspective: Uncovering evidence of military cooperation between the Lebanese government and Hezbollah would give credence to Israeli claims in any future conflict with Hezbollah that the Lebanese state should be held responsible for Hezbollah’s actions. Concern about the consequences of being attributed such responsibility may well deter the Lebanese government from becoming involved in smuggling weapons to Hezbollah.While public sentiment in Israel toward international law is mostly negative and marked by considerable suspicion, this case demonstrates that international law sometimes works in Israel’s favor, and that there is nothing to lose by harnessing the avenues it offers.The writer, Col. (res.) Adv. Liron A. Libman, is a researcher at the Israel Democracy Institute. He previously served as the IDF chief prosecutor and as head of the IDF International Law Department.